mettle vs unconfidence

mettle

noun
  • Good temperament and character. 

  • A quality of endurance and courage. 

adj
  • Spirited, vigorous, stout-hearted. 

unconfidence

noun
  • Absence of confidence; uncertainty; doubt. 

How often have the words mettle and unconfidence occurred in a corpus of books? (source: Google Ngram Viewer )